22 October 2009

MMR vaccine: what are the risks?

The benefits of measles vaccination far outweigh the risks, say international authorities. How true is this statement really? Should parents be concerned about side effects?


At least four people are believed to have died as a result of contracting measles and almost 940 cases have been recorded, mostly in Gauteng, prompting a mass immunisation campaign for people up to the age of 19.

But some South African parents are worried that the vaccines might be dangerous, Sapa reports.

According to the US Centres for Disease Control (CDC) and the World Health Organization (WHO), however, the benefits of vaccination far outweigh the risks.

How true is this statement really? Should parents be concerned about side effects such as Crohn's disease and autism?

The MMR vaccine
This is a triple vaccine against measles, mumps and German measles (rubella) that's often used in the private sector in South Africa. Only the measles vaccine is mandatory for all patients.

We take a look at the benefits and risks associated with this vaccine:

Over a period of four decades, vaccination had eliminated most measles deaths. However, an estimated 745 000 children die every year (about 2000 every day) of the disease which is preventable by a safe, effective and relatively cheap vaccine. Over half of these deaths are in Africa.

One in 1000 children with measles will develop encephalitis. Ten percent of children with measles encephalitis will die. Hundred percent of children who develop subacute sclerosing pan encephalitis (SSPE) will die. Risk of death from measles is five to 15 percent in developing countries, and 0 percent after vaccination.

Concerns: Shock reactions are extremely rare and are usually due to a reaction to gelatin. The risk to develop post infectious encephalomyelitis was less than one per million doses. This is about 1000 times less than the risk to develop this complication from measles itself. Febrile seizures are extremely rare and may occur in 333 per million people.

Transient and benign decrease in platelets occurs in one in 35 000, but will pass without consequences. It was the speculation by one research group that the measles vaccine can be related to autism, that led to major panic among parents.

The alleged associations between measles and autism and Crohn’s disease are based upon weak scientific methods and have been refuted by a large volume of scientifically sound work. The ultimate green light came when 10 of the 12 authors offered a retraction of their controversial 1998 study that claimed a link between the MMR vaccine and autism. The retraction was published in January 2004 in the British medical journal The Lancet, which published the original study.

Measles vaccination is recommended for children with HIV (although not for those severely ill from Aids) because they are at risk for severe measles and they tolerate the vaccine well.

Death from the complication encephalitis is extremely rare. A well known complication is inflammation of the testes, which affect one in four children who get mumps past puberty. This may lead to sterility. About four in 100 people may develop inflammation of the pancreas, which may result in diabetes.

Mumps in the first trimester of pregnancy results in miscarriage in a quarter of cases.

Concerns: One in 100 000 children will develop meningitis after vaccination, but it is mild and without long-term consequences. One in ten children with mumps will develop meningitis.

German measles (rubella):
During the first 18 weeks of pregnancy, when the heart, brain, liver, eyes and other organs are developing, German measles poses a serious risk to the foetus. It can lead to deafness, mental retardation, blindness and other eye defects, and heart defects. There is an 80 percent risk that one or more of these features will occur if the mother contracts the infection in the first trimester of pregnancy.

One in 1500 people with German measles has a bleeding complication due to a drop in blood platelets, and one in 6000 develop encephalitis.

Concerns: Transiental joint symptoms develop in up to 25 percent of post pubertal females due to rubella vaccines. All women of childbearing age should be vaccinated against German measles.

Although vaccination during pregnancy is not advocated, rubella vaccine is of no consequence to the foetus during pregnancy, according to WHO experts.

(Health24, October 2009)

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Sources: The South African National TB Association; Sapa




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